Caption: Asteroid impact in planet-forming region. Computer artwork showing the immediate aftermath of a large asteroid impact around the sun-like star NGC 2547-ID8. This 35-million-year-old star is thought to be forming rocky planets. Rocky planets begin life as dusty material circling around young stars. The material clumps together to form asteroids that ram into each other (as here). Although the asteroids are often destroyed, some grow over time and transform into proto-planets. After about 100 million years, the objects mature into full-grown terrestrial planets. The Moon is thought to have formed from a giant impact between proto-Earth and a Mars-size object. Image based on data obtained by NASA's Spitzer Space Telescope.